American
soccer has a whole set of these. The NASL, as mentioned above, died; there's also the
Major Indoor Soccer League and all the sundry members of the
United Systems of Independent Soccer Leagues -- the
USISL Select League, the
USISL Premier League, and some other
Division 3 league. They were all munched when
Major League Soccer, the
A-League and the
USISL merged under the
United Soccer Leagues banner, which preserved MLS, the A-League and a league called the
D3 Pro League below the A-League. Some Select and Premier League cities saw their teams move up to the A-League, the rest just saw them
relegated to D3 status.
In American football, the World League of American Football could qualify under this category, since 7 of its 10 teams (those based in the U.S. and Canada) died when it became NFL Europe in 1995 (the WLAF suspended operations after summer 1992).
A host of baseball minor leagues have died, but the American Association rates special attention; it started in the 1880s as a major league competitor to the National League, and was a AAA league until 1997. When the major leagues expanded in 1998, two teams were added to the AAA ranks (the Durham Bulls and the Memphis Redbirds), one team relocated (the Phoenix Firebirds became the Fresno Grizzlies), and the AA disbanded, sending three of its teams to the International League and five to the Pacific Coast League.